In a manufacturing process of a semiconductor device, a plasma processing apparatus is used to perform a predetermined processing such as etching and/or CVD film formation on a semiconductor wafer to be processed (hereinafter referred to as a wafer) by using a plasma. In such plasma processing apparatus, the wafer is mounted on a mounting table or a lower electrode installed in a plasma processing container in vacuum, a plasma is generated in the processing container and a predetermined plasma processing is executed on a surface of the wafer by the plasma.
There has been known a scheme that by applying a high frequency power to the mounting table on which the wafer is mounted or to a lower electrode embedded therein, negative self-bias voltage (VDC) is generated at the mounting table or the lower electrode, and ions in the plasma are attracted toward the wafer by the self-bias voltage to thereby accelerate the plasma processing. In this case, the self-bias voltage largely influences an incidence angle and an energy of the ions impinging onto the wafer. While performing a plasma etching process, for example, an excessively high self-bias voltage causes the surface of the wafer to be damaged, whereas an excessively low self-bias voltage causes reactions of the ions to be insufficient. Thus, in order to perform a proper plasma processing, it is preferable to detect the self-bias voltage during the plasma processing to adjust a magnitude of the self-bias voltage.
In Japanese Patent Laid-open Publication No. 1996-335567, there is disclosed a scheme in which there are provided a lower electrode for mounting a wafer thereron and a measuring electrode disposed around the wafer and connected to the lower electrode; and the self-bias voltage is measured at a power supply path through which a high frequency power is applied to the lower electrode.
However, when using a mounting table wherein a surface of the electrode to which a high frequency voltage is applied is covered by an insulator, it becomes inappropriate to measure, as in the Japanese Patent Laid-open Publication No. 1996-335567, the self-bias voltage at the power supply path of the electrode to which the high frequency power is applied, and the self-bias voltage is not detected until the electrode is exposed to the plasma, e.g., through cracks which may be generated in the insulator. Therefore, the self-bias voltage is merely interlockingly used only to indicate a presence of cracks in the insulator in case of using such a mounting table.